In FIGS. 10a and 10b of U.S. Pat. No. 5,966,641 (PLANTRONICS), there are shown top and side plan views, respectively; of a twin-axis magnetic inductive aerial that includes a permeable core 1002 and first and second windings 1004 and 1006. The core 1002 is box shaped and formed of ferrite. The first winding 1004 is disposed on the surface of the core 1002 in a first plane. The second winding 1006 is disposed in a second plane perpendicular to the first plane. The windings 1004 and 1006 are oriented to minimize mutual inductance. The physical construction of the windings 1004 and 1006 provide this minimization which negates any need for additional mechanical fixing or adjustment, for nulling. In most applications, such a structure is therefore described as self-nulling. The dimensions of the core 1002 are selected so that the windings 1004 and 1006 have substantially identical inductance and capacitance.
U.S. Pat. No. 6,407,677 (VALEO) discloses a device for low-frequency communication by magnetic coupling, comprising an emitter placed in a vehicle and a receiver placed in an identification member, wherein one of the emitter or the receiver includes a loop antenna, the other of the emitter or the receiver includes three associated coils wound around three perpendicular axes defining a trihedral and creating an omnidirectional magnetic field, and the three associated coils are supplied with currents of like frequency, 60 degrees or 120 degrees out of phase relative to each other. The here associated coils are wind on one another around six faces of a parallelepiped, common magnetic core.
ES 2200652 (PREDAN) discloses a three-dimensional hybrid antenna comprising a rectangular shaped monolithic magnetic core, with three mutually orthogonal windings arranged so that the antenna receives a signal in each of the windings when is subjected to a low frequency electromagnetic field. Furthermore, the magnetic core is adhesively bonded to a plastic base, being said plastic base provided with terminals on its bottom side for interconnection between the windings arranged surrounding the core and external systems.
WO 2014072075 (PREMO) discloses a three-dimensional antenna with a magnetic core and three windings 21, 22 and 23 wound around three mutually orthogonal axes, each of said windings surrounding said core 10 and relate to arrangements of windings on a magnetic core and their connections between the windings core and a PCB acting as a support plate.
As known in the art, for a given inductance having a fixed number of turns N, a given form of a core on which is wound, a fixed operating frequency and a known permeability magnetic material with a winding of a given section length and electrical resistivity, the lower the total capacity distributed the greater will be the value of Q.
In high frequencies coils it is necessary that they do not enter in auto resonance at frequencies close to the frequency of operation. To solve this a usual practice has been to design coils having a resonance frequency one order of magnitude above the frequency of operation. For this the values of the inductive and capacitive impedance are calculated to be equal in magnitude and opposite in angle to the auto-resonance frequency. In order to be able to work at high operating frequencies in radio and television systems, medium wave coils, and RF tuned pots, it is a usual practice from the 1950s to the 1970s to use multi-section coil-formers on which the winding is coiled by splitting it to reduce the distributed capacity and so raising the Q factor so that the resonance frequency being maximum.
An example of this technique can be found on EP2360704B1 (SUMIDA) that relates to an antenna coil with a cross shaped core and at least three series windings per branch to reduce de distributed capacity and increase the resonance frequency and the Q-factor.
Document U.S. Pat. No. 9,647,340B2 (TOKO) describes a tri-axial antenna having a magnetic core defining X-axis, Y-axis and Z-axis, said antenna including an X-axis coil wound around the X-axis, a Y-axis coil wound around the Y-axis, and a Z-axis coil wound around the Z-axis. According to this document each coil includes two parallel and symmetric partial coils.
The magnetic core described in this document has four protuberances on the four corners defining two orthogonal winding channels for containing the X-axis coil and for containing the Y-axis coil, but the outer perimeter of the magnetic core lacking winding channel for containing the Z-axis coil.
The magnetic core is inserted within a support structure which defines two parallel winding channels for containing the Z-axis symmetric partial coils. Said support structure is also partially interposed between the X-axis coil and the magnetic core, and also between the Y-axis coil and the magnetic core, said support structure including partition walls spacing apart the symmetric partial coils.
Said support structure spaces the coils from the magnetic core, but produces an increase of the coil length, and introduces parasitic capacities reducing the quality factor of the antenna.
The present invention has been made in view of providing an alternative solution to the ones existent in the art to obtain a three-axis antenna with a high gain by an increase of the Q factor based on a special core on which the three orthogonal coils are directly wind and at least two of said coils being separated by partitions walls of the own core. The proposed solution also provides miniaturization and space saving.